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Corticofugal projection patterns of whisker sensorimotor cortex to the sensory trigeminal nuclei.

Smith JB, Watson GD, Alloway KD, Schwarz C, Chakrabarti S - Front Neural Circuits (2015)

Bottom Line: We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex.Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences.Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Science and Mechanics, Pennsylvania State University University Park, PA, USA ; Center for Neural Engineering, Huck Institute of Life Sciences, Pennsylvania State University University Park, PA, USA.

ABSTRACT
The primary (S1) and secondary (S2) somatosensory cortices project to several trigeminal sensory nuclei. One putative function of these corticofugal projections is the gating of sensory transmission through the trigeminal principal nucleus (Pr5), and some have proposed that S1 and S2 project differentially to the spinal trigeminal subnuclei, which have inhibitory circuits that could inhibit or disinhibit the output projections of Pr5. Very little, however, is known about the origin of sensorimotor corticofugal projections and their patterns of termination in the various trigeminal nuclei. We addressed this issue by injecting anterograde tracers in S1, S2 and primary motor (M1) cortices, and quantitatively characterizing the distribution of labeled terminals within the entire rostro-caudal chain of trigeminal sub-nuclei. We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex. Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences. Whereas S1 projection terminals tend to cluster within the principal trigeminal (Pr5), caudal spinal trigeminal interpolaris (Sp5ic), and the dorsal spinal trigeminal caudalis (Sp5c), S2 projection terminals are distributed in a continuum across all trigeminal nuclei. Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

No MeSH data available.


Related in: MedlinePlus

Three cases showing the distribution of retrogradely labeled cells in cortex following FG deposits at different rostrocaudal positions in the trigeminal sensory nuclei. (A) FG deposit into the Sp5ir. (A′) Digital reconstruction of retrogradely labeled cells in cortex superimposed on an outline of layer IV barrels and septa. Schematic shows the average distribution of binned terminals across the different trigeminal sensory nuclei (taken from Figure 5) with the location of the current injection marked with an asterisk. (B–C′) Identical plots for two other cases receiving tracer deposits into the Sp5ic and the Sp5ic/Sp5c boundary.
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Figure 7: Three cases showing the distribution of retrogradely labeled cells in cortex following FG deposits at different rostrocaudal positions in the trigeminal sensory nuclei. (A) FG deposit into the Sp5ir. (A′) Digital reconstruction of retrogradely labeled cells in cortex superimposed on an outline of layer IV barrels and septa. Schematic shows the average distribution of binned terminals across the different trigeminal sensory nuclei (taken from Figure 5) with the location of the current injection marked with an asterisk. (B–C′) Identical plots for two other cases receiving tracer deposits into the Sp5ic and the Sp5ic/Sp5c boundary.

Mentions: We injected the ventral depths of Sp5ir and the Sp5ic/Sp5c boundary of two animals to test whether the pattern of corticofugal projections revealed by our anterograde tracing experiments were confirmed by retrograde labeling. Data from these two animals along with a third case that received FG in Sp5ic are shown in Figure 7. The injections in Figures 7A–C targeted the Sp5ir, Sp5ic and Sp5ic/Sp5c boundary respectively. As shown earlier in Figure 6, every injection resulted in retrogradely labeled cells in the Sp5ic and Sp5c. These intra-trigeminal projection neurons have been reported before and have been shown to be primarily inhibitory interneurons (Avendaño et al., 2005; Furuta et al., 2010; Martin et al., 2014).


Corticofugal projection patterns of whisker sensorimotor cortex to the sensory trigeminal nuclei.

Smith JB, Watson GD, Alloway KD, Schwarz C, Chakrabarti S - Front Neural Circuits (2015)

Three cases showing the distribution of retrogradely labeled cells in cortex following FG deposits at different rostrocaudal positions in the trigeminal sensory nuclei. (A) FG deposit into the Sp5ir. (A′) Digital reconstruction of retrogradely labeled cells in cortex superimposed on an outline of layer IV barrels and septa. Schematic shows the average distribution of binned terminals across the different trigeminal sensory nuclei (taken from Figure 5) with the location of the current injection marked with an asterisk. (B–C′) Identical plots for two other cases receiving tracer deposits into the Sp5ic and the Sp5ic/Sp5c boundary.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4588702&req=5

Figure 7: Three cases showing the distribution of retrogradely labeled cells in cortex following FG deposits at different rostrocaudal positions in the trigeminal sensory nuclei. (A) FG deposit into the Sp5ir. (A′) Digital reconstruction of retrogradely labeled cells in cortex superimposed on an outline of layer IV barrels and septa. Schematic shows the average distribution of binned terminals across the different trigeminal sensory nuclei (taken from Figure 5) with the location of the current injection marked with an asterisk. (B–C′) Identical plots for two other cases receiving tracer deposits into the Sp5ic and the Sp5ic/Sp5c boundary.
Mentions: We injected the ventral depths of Sp5ir and the Sp5ic/Sp5c boundary of two animals to test whether the pattern of corticofugal projections revealed by our anterograde tracing experiments were confirmed by retrograde labeling. Data from these two animals along with a third case that received FG in Sp5ic are shown in Figure 7. The injections in Figures 7A–C targeted the Sp5ir, Sp5ic and Sp5ic/Sp5c boundary respectively. As shown earlier in Figure 6, every injection resulted in retrogradely labeled cells in the Sp5ic and Sp5c. These intra-trigeminal projection neurons have been reported before and have been shown to be primarily inhibitory interneurons (Avendaño et al., 2005; Furuta et al., 2010; Martin et al., 2014).

Bottom Line: We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex.Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences.Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Science and Mechanics, Pennsylvania State University University Park, PA, USA ; Center for Neural Engineering, Huck Institute of Life Sciences, Pennsylvania State University University Park, PA, USA.

ABSTRACT
The primary (S1) and secondary (S2) somatosensory cortices project to several trigeminal sensory nuclei. One putative function of these corticofugal projections is the gating of sensory transmission through the trigeminal principal nucleus (Pr5), and some have proposed that S1 and S2 project differentially to the spinal trigeminal subnuclei, which have inhibitory circuits that could inhibit or disinhibit the output projections of Pr5. Very little, however, is known about the origin of sensorimotor corticofugal projections and their patterns of termination in the various trigeminal nuclei. We addressed this issue by injecting anterograde tracers in S1, S2 and primary motor (M1) cortices, and quantitatively characterizing the distribution of labeled terminals within the entire rostro-caudal chain of trigeminal sub-nuclei. We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex. Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences. Whereas S1 projection terminals tend to cluster within the principal trigeminal (Pr5), caudal spinal trigeminal interpolaris (Sp5ic), and the dorsal spinal trigeminal caudalis (Sp5c), S2 projection terminals are distributed in a continuum across all trigeminal nuclei. Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

No MeSH data available.


Related in: MedlinePlus